A black hole is a volume from which photons, or any matter, can not escape. More formally, the coordinate speed of light at the event horizon - the boundary of a black hole - is zero, as measured by a sufficiently separated observer.

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Why does the Ricci tensor vanishes in Schwarzschild metric? [duplicate]

If the Schwarzschild metric is suppose to describe the behaviour of a spherical object in flat space, so the Schwarzschild is different from the flat metric because it describes curved space so why ...
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Do neutrinos of any flavor get trapped in black holes?

This question has been bothering me a bit. I know that neutrinos have super small mass and they interact via the weak force. Since they have a non-zero mass, they should be affected by black holes and ...
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How could the “Big Bang” singularity have actually expanded? [duplicate]

We have mountains of evidence about singularities and how they work, and we have mountains of evidence that the "Big Bang" was the origin of the universe as we know it. But if compressing enough ...
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Why can't no particle rotate opposite to the central mass within the ergosphere?

Wiki says about the Kerr metric: A moving particle experiences a positive proper time along its worldline, its path through spacetime. However, this is impossible within the ergosphere, where ...
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Big Bang snuffed by a black hole?

Wasn't the density of the universe at the moment after the Big Bang so great as to create a black hole? If the answer is that the universe/space-time can expand anyway what does it imply about what ...
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Eternal Black Hole: Connection with White Holes

What is the connection between an eternal black hole and a white hole? No prior knowledge of general relativity.
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Penrose diagram (Reissner-Nordstrom metric)

I try to derive the Penrose diagram for the Reissner-Nordstrom metric $$ \text d s^2 = -\frac{(r-r_+)(r-r_-)}{r^2}\text d t^2 + \frac{r^2}{(r-r_+)(r-r_-)}\text d r^2 + r^2 \text d \Omega^2\;,\qquad ...
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White Hole Formation and Queries

How do white holes form? Why are they called the "time-reversed" versions of a black hole? What's an "eternal" black hole? How come a white hole is only encountered if you remove the star from the ...
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What am I missing in this thought experiment about a black hole?

I've got a problem setting up a general relativity (GR) thought experiment. Thanks for your help! I'm the observer, in a lab that is falling through the event horizon of a black hole, observing a ...
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How close can an observer approach the black hole in an unpowered flyby without falling into it?

In classical mechanics by choosing the right trajectory you can approach a planet arbitrarily closely, if there is no atmosphere or anything to slow you down, you can approach the surface then fly ...
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Why singularity in a black hole, and not just “very dense”?

Why does there have to be a singularity in a black hole, and not just a very dense lump of matter of finite size? If there's any such thing as granularity of space, couldn't the "singularity" be just ...
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White Hole Formation [duplicate]

How does a white hole form in nature if it were to exist? No knowledge of general relativity or advanced mathematics but doing a researching a physics project and need a basic explanation.
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Really nothing special when falling into a black hole?

It has been said time and again, that an observer who falls into a black hole will not notice anything special. Is this really true? There is of course the problem with the tidal forces, but I ...
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No hair theorem and black hole entropy

The no hair theorem says that black holes rapidly converge to a state that is completely described just by their mass, spin and charge. Black hole thermodynamics says that the black hole entropy is ...
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178 views

Does compression of matter increase gravity?

Black holes are thought to originate when a star burns out and collapses to a smaller physical size. This compresses it's matter, but would that increase it's gravity? And would it be enough to ...
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1answer
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Hawking radiation (black hole evaporation) [duplicate]

I understand that one of the simplified ways of looking at Hawking radiation is a pair of virtual particles close to the event horizon (but outside of it). The particle with negative energy falls into ...
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What is the physical meaning of fact, that Reissner-Nordstrom black hole is thermodynamically unstable?

It is known, that Reissner-Nordstrom black hole is thermodynamically unstable [1]. Does it mean, that there is no Reissner-Nordstrom black hole in physical world? Does it mean, that there may be ...
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3answers
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Black Hole Gravity

Let's say I'm orbiting a black hole at a great distance. Then something happens. On the far side of the black hole, a neutron star of significant mass merges with my black hole. Will I ever know it ...
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Should all theories of gravity have Schwarzschild solution?

A consistent theory of gravity must include the Newton's classical theory of gravity as a weak field approximation. Moreover, to satisfy the experiments in the solar system, the Schwarzschild ...
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Can a free falling observer localize the event horizon by calculations?

I'm think that in general relativity we can always pass the one curve in one coordinate system for another coordinate system. My intuition say that the free falling observer locate the event horizon ...
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Is black hole complementarity compatible with canonical quantization?

Suppose at time $t$, Alice and Bob are hovering just outside the event horizon of a black hole, sharing the same position, velocity and acceleration. Shortly afterward, in less than the Schwarzschild ...
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Schwarzschild Solution Convention

In looking at the components of the Schwarzschild Metric, one finds $ g_{00} = (1 - \frac{r_s}{r})c^2 $. Wikipedia states that $r$ is measured as the circumference, divided by $2π$, of a sphere ...
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611 views

Surface gravity of Kerr black hole

I'm going through Kerr metric, and following the 'Relativist's toolkit' derivation of the surface gravity, I've come to a part that I don't understand. Firstly, the metric is given by ...
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Introductions to no-hair theorem(s)

I wanted to ask if anyone can provide a reference that is an introduction on the no-hair theorem(s) (conjecture(s)). Review papers on the topic would be gratefully accepted as well. I have already ...
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Is a black hole really a hole in space? [closed]

What if when a supernova occurs, instead of it condensing into a singularity it creates enough force to tear a hole into the fabric of space? Is a black hole just what is sounds like, a hole in space? ...
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Paradox of nesting black holes and release of energy

By dumping a gas cloud into a small black hole, I can produce radiation energy, this is how quasars produce energy. By dumping the previous black hole, with the gas cloud inside, into a black hole, ...
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Binary Singularity?

When two black holes collide, if the singularities were very small they would never merge together. they would rotate very fast as something other than a disk. The event horizon would oscillate very ...
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What is Hawking radiation and how does it cause a black hole to evaporate?

My understanding is that Hawking radiation isn't really radiated from a black hole, but rather occurs when a particle anti-particle pair spontaneously pop into existence, and before they can ...
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Why does my apple not weigh 500 tons?

Related to this question: What is potential energy truly? $E=mc^2$ - energy equals mass. So, if an object has gravitational potential energy relative to another object, it should have additional mass ...
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Seeing the shadow of a black hole

Why can't we see the shadow of a black hole cast on earth. Shouldn't the black hole block some light from a star or a galaxy far behind as they line up.
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What are the equations of motion that model near light speed orbits of a massive body about incredibly massive bodies?

In Kip Thorne's recently published book, The Science of Interstellar, he describes, by means of an illustration, the complex nature of a spacecraft orbiting a massive black hole with velocities ~ ...
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Eternal Black Holes

What is the definition of an eternal black hole? Studying white holes and the term appears in relation to this field of research.
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40 views

why are chemical reactions the same at different gravity levels

Are all chemical reactions the same at a quantum level in different levels of gravity? How does the mass of subatomic particles change atomic behaviour at different gravity, in terms of speed and ...
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22 views

Evaporation of a black hole [duplicate]

What happens to the singularity within a black hole when a black hole evaporates? If there is a point in space which is both infinitely dense and small, do they simply evaporate as well?
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Does the escape velocity of a black hole exceed $c$ *before* a singularity is created?

As an offshoot of the question Can we have a black hole without a singularity? I'm curious if the point of no return at which the massive object is condemned to become a singularity happens before its ...
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geometry inside the event horizon

I'm trying to understand intuitively the geometry as it would look to an observer entering the event horizon of a schwarszchild black hole. I would appreciate any insights or corrections to the above. ...
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How can a black hole increase mass? [duplicate]

As far as I know, the time dilation at the event horizon of a black hole is infinite, so everything falls asymptotically towards, but never reaching, the horizon for an outside observer. How then can ...
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3answers
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Surface waves on Dr. Miller's planet

In the movie 'Interstellar', the crew land on a water world orbiting a black hole. The gravity is greater than that of Earth and there are huge surface waves present in the ocean that they land in. ...
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Can we have a black hole without a singularity?

Assuming we have a sufficiently small and massive object such that it's escape velocity is greater than the speed of light, isn't this a black hole? It has an event horizon that light cannot escape, ...
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1answer
226 views

What is the largest disparity of gravitational time dilation from earth's that life can survive?

In certain theoretical scenario's a human can be in a gravitational field where he would age half as fast as on earth's surface. However, for light to travel half as fast in one direction, we are ...
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1answer
48 views

What are the virtual particles generated during the Hawking radiation?

What are the virtual particle pairs generated during the Hawking radiation? If a photon is emitted by Hawking radiation, what is its negative energy partner which fell into the black hole? Does it ...
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Thought Experiment - Poking a stick across a Black Hole's Event Horizon

The classical explanation of a black hole says that if you get to close, you reach a point - the event horizon radius - from which you cannot escape even travelling at the speed of light. Then they ...
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Extended object passing near an event horizon

Suppose a physically realistic object of nontrivial size (such as a star) passes by a black hole. The center-of-mass trajectory for the object is hyperbolic and (therefore) completely outside the ...
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What happens at the center of a black hole according to holographic theory?

As far as I understand, the AdS/CFT correspondence proposed by Maldacena is an exact duality to a four-dimensional theory, which interpolates between one well-defined conformal field theory in the UV ...
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23 views

'Dipping' an object beyond an event horizon [duplicate]

Say I'm hovering just outside an event horizon, what would happen if I held onto a stick and dipped half of it beyond the EH? Would I be pulled in? Would the portion of the stick beyond the EH be cut ...
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53 views

Gravitational singularity

Is it possible that the gravitational singularity actually turns out to be a genuine singularity once we have a true theory of quantum gravity in place. There is a lot of talk about singularity but ...
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If perfect maximal entanglement is never true, does a remainder invalidate the monogamy of entanglement?

If something is only very nearly (and/or observed to be) maximally entangled, does that remainder allow for a menage trois of hybrid correlation (as it relates to AMPS)?
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Why would a black hole explode?

It is common in popular science culture to assume that Hawking radiation causes black holes to vaporize. And, in the end, the black hole would explode. I also remember it being mentioned in A Brief ...
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164 views

Hawking Radiation and virtual particles

Why is energy/ mass taken away from a black hole? Doesn't the energy coming from the virtual particle come from the vacuum energy? ...if this is so, why does the black hole have to pay the energy ...
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Can gravitaitonal waves orbit each other to form a standing wave?

Since gravity waves are a type of propagation of energy of some sort, they ought to induce their own gravitational field. I'm assuming this extra gravitational force / curvature is independent from ...